Toyota Repair: Toyota Defroster mode, vacuum control, heat vents

Question
Thank you, Ted for taking questions.  My Toyota is a 94 Camry 4.4 w/AC. My problem is when I switch the selector to defrost nothing happens. Air continues to flow out of the main vents.  The main vents, heat vents and temperature seem to be working fine just nothing will divert up to the defrost vents at the windshield.  By the way, there is no hissing noise in any setting if vacuum control is involved.  Can you tell me what the problem may be and where to look for it.

Thanks
Ron

Answer
There may be a cable that controls the air door that has come off, you can check under the left side of the dash underneath, pull the carpet back, work the defrost control knob and see if the cable is moving the blend door, it may have come off and needs to be reattached.